Mass flow controller and method of operation of mass flow controller

ABSTRACT

A mass flow controller has a sensor section that generates an electrical signal, dependent on the measured flow rate. The controller sends a control signal to a magnetic field generating unit, dependent upon the actual flow rate and the desired flow rate, which in response, generates a magnetic flux in the direction of the fluid input to the fluid output through the body of the controller. This means that the magnetic flux is concurrent with the fluid flow within the mass flow controller body. The magnetic flux alters the position of a plunger button assembly, located between the bypass chamber and the fluid output, relative to an orifice plate to control the flow rate to obtain the desired output flow. By incorporating the proportional control valve within the mass flow controller body, the need for a separate and large valve section is eliminated, reducing the size and cost of the controller.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part application of commonly-owned U.S. patentapplication Ser. No. 09/517,391, filed Mar. 2, 2000, now U.S. Pat. No.6,314,991.

FIELD OF THE INVENTION

The present invention relates to mass flow controllers.

DESCRIPTION OF RELATED ART

Mass flow controllers are known in the art for controlling the specificamount of flow of a fluid, necessary for a particular process, e.g., insemiconductor manufacturing processes, such as chemical vapor depositionor the like. Mass flow controllers are known to be capable of sensingthe flow occurring through the controller and modifying or controllingthat flow as necessary to achieve the required control of the mass ofthe fluid delivered to the particular process.

Sensing the flow is a function of the type of fluid utilized and thephysical effect used to sense the amount of flow. One typical type ofphysical effect to sense mass flow is to measure the temperaturedifferential between the upstream and downstream heater/sensor coilsexposed to the fluid flow. Other systems may use absolute and/ordifferential pressure changes, light absorption, or the momentum change(e.g., paddle wheel) to measure the flow.

Modifying or controlling the flow is typically made in response to thesensed flow as it relates to the desired flow by modifying across-sectional opening area available to the fluid for flowing. Thesmaller the area available for flow, the smaller the mass flow, andvice-versa. In the past, this has been accomplished with a typicalplunger/diaphragm/orifice system. An orifice provides the variable crosssectional opening area for flow, where the flow control is dictated bythe positioning and motion of a plunger/diaphragm or needle stem in theorifice in response to a flow control signal. The flow control signal isgenerated in response to the measurement of the flow sensor.

A servo control section generates a control signal that drives thepositioning of the plunger/diaphragm or needle stem, typically throughthe use of a solenoid type of driver. The solenoid driver has aferromagnetic core surrounded by a coil. The plunger/diaphragm,typically made of ferromagnetic material, is held close to the orificeby a spring. The energizing of the coil generates a magnetic field thatpulls the plunger/diaphragm away from the orifice while the spring pullsit toward the orifice. The distance between the orifice and theplunger/diaphragm is dependent upon the relative strengths of themagnetic field and the spring. The proportional control valve by itsnature is not an open and shut valve. The closer the needle stem orplunger/diaphragm is to the orifice, the more restricted the flowbecomes, until the flow is shut off, and the more it is withdrawn themore the flow increases, until it no longer affects the amount of flow.

For precision control, complex and expensive controller circuitry isneeded to control the positioning and movement of the needle stem orplunger/diaphragm as the flow is regulated. The valve parts themselvesmust be manufactured with high precision, and are therefore expensive.In addition, prior art proportional controlled solenoid valve mass flowcontrollers require the needle stem or plunger/diaphragm to be mountedat right angles to the fluid flow direction. Consequently, the orificeis also mounted at right angles to the fluid flow path, and the fluidhas to change direction to go through the orifice, which generatesturbulence in the fluid.

Often the mass flow controller, particularly when used in high precisionsemiconductor manufacturing processes and the like, is part of a toolthat has limited space available for the flow controllers, particularlyif there are multiple mass flow controllers that are positioned in theimmediate area of the actual discharge of the fluid into the tool'sprocess chamber.

There is a need in the art, therefore, for a mass flow controller thatis simpler, less expensive, smaller, and easier to manufacture andcontrol.

SUMMARY OF THE INVENTION

The present invention, according to one embodiment, utilizes a closedloop magnetic flux path passing through the body of the controller inthe direction of flow from its input to its output to magneticallyoperate a flexible plunger button valve assembly that is normally springbiased into the shut position. A current generated from a servo controlsection of a mass flow controller generates magnetic flux to pull theplunger valve assembly away from an orifice and allow more fluid to flowthrough. By controlling the amount of flux generated, and thereby thepositioning of the button valve assembly relative to the orifice, theflow through the orifice can be controlled. Consequently, a largeseparate proportional control valve section is no longer necessary,which results in a more compact, less expensive and more reliable massflow controller that is less costly to manufacture and has fewercomponents than the conventional mass flow controllers discussed above.

The present invention will be more fully understood upon considerationof the detailed description below, taken together with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a mass flow controller of the prior art;

FIG. 1B shows magnetic flux path through a mass flow controller of FIG.1A;

FIG. 2 shows an exploded view of the mass flow controller of FIG. 1A;

FIG. 3A shows a mass flow controller according to one embodiment of thepresent invention;

FIGS. 3B-1 and 3B-2 show side and front views, respectively, of a bypassassembly of FIG. 3A according to one embodiment;

FIGS. 3C-1 and 3C-2 show side and front views, respectively, of a secondembodiment of a bypass assembly;

FIGS. 3D-1 and 3D-2 show side and front views, respectively, of a thirdembodiment of a bypass assembly;

FIGS. 3E-1 and 3E-2 show side and front views, respectively, of a fourthembodiment of a bypass assembly;

FIGS. 3F-1 and 3F-2 show side and front views, respectively, of a fifthembodiment of a bypass assembly;

FIG. 3G shows a side view of a sixth embodiment of a bypass assembly;

FIG. 3H shows magnetic flux path through a mass flow controller of FIG.3A;

FIG. 4 shows an exploded view of the mass flow controller of FIG. 3A;

FIG. 5 shows a sectional view of the mass flow controller of FIG. 3Aalong sectional line A-A′;

FIG. 6A shows a side view of the button assembly and orifice plate shownin FIGS. 3A and 4;

FIG. 6B shows a side view of the button assembly and orifice plateaccording to another embodiment;

FIGS. 7A and 7B show different configurations of an orifice plate; and

FIG. 7C shows a side view of an orifice plate and button plungerassembly;

FIG. 8 shows an exploded view of a mass flow controller according toanother embodiment of the present invention;

FIG. 9 shows magnetic flux path through a mass flow controller accordingto another embodiment of the present invention;

FIG. 10 shows magnetic flux path through a mass flow controlleraccording to yet another embodiment of the present invention;

FIG. 11 shows a mass flow controller according to another embodiment ofthe present invention;

FIG. 12 shows the mass flow controller of FIG. 11, rotated 90° about thevertical axis;

FIG. 13 shows the mass flow controller of FIG. 11 with securing screws;

FIG. 14 shows an exploded view of a portion of the mass flow controllerof FIG. 11, rotated 90° about the axis perpendicular to the verticalaxis;

FIGS. 15 and 16 show a portion of the bypass assembly according to twoembodiments of the present invention;

FIG. 17 shows a plunger button assembly according to one embodiment;

FIG. 18 shows an orifice plate according to one embodiment; and

FIG. 19 shows the magnetic flux path through the mass flow controller ofFIGS. 11 and 12.

Use of the same reference symbols in different figures indicates similaror identical items.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A and 2 show a conventional mass flow controller 10. FIG. 1Ashows an assembled controller 10, while FIG. 2 shows an exploded view ofparts of controller 10. Mass flow controller 10 has three main sections:a sensor section 20, a valve section 30, and a mass controller blocksection 40. A fluid input fitting 11 and a fluid output fitting 12 aresealed to respective input and output ends of block section 40 throughmetal O-rings 13. Note that other seals are also suitable, such as knifeedge, O-ring, C-ring, and flat gasket, made of materials such as metal,polymer, and elastomer. A cover 14 enclosing sensor section 20 and valvesection 30 is secured to input and output fittings 11 and 12 by screws15.

Gas or fluid enters input fitting 11 through an opening 16 in inputfitting 11. The flow of fluid through mass flow controller 10 is shownin the dark lines in FIG. 1A. Opening 16 opens into a bypass assembly17, which has an input plenum 18 and an output plenum 19, and which islocated within block section 40. Sensor section 20 is secured to blocksection 40 via appropriate seals 22. While a majority of the fluidpasses along bypass assembly 17, a portion of the fluid travels throughsensor section 20 along a sensor tube 23. Bypass assembly 17 restrictsthe flow of fluid along one of a plurality of channels or grooves formedin the generally cylindrical outer surface of bypass assembly 17 andinto output plenum 19. As is known in the art, this is for the purposeof generating a laminar flow such that a portion of the fluid passingfrom input plenum 18 into a sensor bypass line 21 and into sensorportion 20 is linearly proportional to the fluid passing from inputplenum 18 to output plenum 19 through the plurality of channels orgrooves in bypass assembly 17.

Sensor section 20 typically includes multiple coils 24 wrapped aroundsensor tube 23. When fluid flows inside sensor tube 23 from a heatedupstream coil to a heated downstream coil that are electricallybalanced, thermal energy is transferred from the coils to the flowingfluid. The amount of thermal energy transferred from the coils to thefluid is inversely proportional to the fluid temperature. Thermal energytransfer from the upstream coil and the downstream coil to the fluid isdisproportionate because the fluid temperature is different at theupstream coil than at the downstream coil. This difference in heattransfer from the upstream coil and the downstream coil results in atemperature differential between the coils which manifests as a changein the relative resistance of the two coils. This change in resistanceis directly proportional to the amount of fluid flowing through sensortube 23. Typically, a resistor circuit (not shown), which is coupled tothe upstream and downstream coils, is configured to form a balancedbridge network when there is no fluid flow. When the fluid flows, theresistance in the coils changes. The bridge network measures the changeof the resistance in the coils and generates a signal corresponding tothe flow of fluid through sensor tube 23.

Fluid from bypass assembly 17 and sensor tube 23 converge and flow intoa fluid flow path 25. Fluid travels along fluid flow path 25, throughvalve section 30, and out through an opening 26 in output fitting 12.Valve section 30 includes an upper housing 31 enclosing a wound coilassembly 32 of a solenoid valve, which consists of a pole assembly orplug 33. Pole assembly 33 has a lower housing 34, which together withupper housing 31, are secured to block section 40 and sealed with anO-ring 35 or other appropriate seal. A plunger button assembly 37,having a flat sealing surface 46, is held in a cavity in lower housing34 of pole assembly 33 by a plunger button capture ring 36. Plungerbutton capture ring 36, plunger button assembly 37, and a plunger buttonassembly pre-tensioning ring 38 are in abutting relation to an orificeplate 39, which is sealed to block portion 40 by an O-ring 41 or otherappropriate seal.

Orifice plate 39 has an opening 42 into which fluid flows from fluidflow path 25, where the flow of the fluid is controlled by the positionof the plunger button assembly 37, relative to orifice opening 42. Therelative position of plunger button assembly 37 is controlled bymagnetic flux generated in core 33 in response to the signal generatedfrom sensor block 20. Coil 32 is held in place by a top cap 43 and apole nut 44. Top cap 43 is sealed with an O-ring 45. FIG. 1B shows themagnetic flux path of controller 10. As seen from FIG. 1B, the magneticflux only travels through valve section 30 to control the position ofplunger button assembly 37, and not through either sensor section 20,bypass assembly 17, or block 40.

FIGS. 3A and 4 show a mass flow controller 300 according to oneembodiment of the present invention. FIG. 3A shows an assembledcontroller 300, while FIG. 4 shows an exploded view of parts ofcontroller 300. Mass flow controller 300 includes an input fitting 311attached to an input magnetic flux plate 312, typically made offerromagnetic material, where both input fitting 311 and input magneticflux plate 312 have an opening 313 through which fluid enters and anoutput fitting 314 attached to an output magnetic flux plate 315,typically made of ferromagnetic material, where both output fitting 314and output magnetic flux plate 315 have an opening 316 through whichfluid exits. A mass controller block 320, typically made ofnon-ferromagnetic material, is sealed between input magnetic flux plate312 and output magnetic flux plate 315 by O-rings 321 or otherappropriate seals, which can be metal, plated metal, polymeric, orelastomeric material.

Fluid flows through opening 313 into a bypass assembly 317, typicallyformed with a ferromagnetic material, via distribution holes 318. Bypassassembly 317 can be a single part with longitudinal grooves or channels350 formed directly thereon, or in other embodiments, bypass assemblycan be formed from more than one part, as shown in FIGS. 3B-1 and 3B-2.For example, bypass assembly 317 can be formed from an inner core 355and an outer sleeve 360 having grooves 350 formed along the outerperimeter. Inner core 355 can be of a ferromagnetic material, whileouter sleeve 360 can be of a non-magnetic material. In anotherembodiment, inner core 355 is made of a non-magnetic material, and outersleeve 360 is made of a ferromagnetic material.

Other embodiments of bypass assembly 317 are shown in FIGS. 3C-1 and3C-2 to 3F-1 to 3F-2, and 3G, where “-1” indicates a side view and “-2”indicates a front view. In each of these embodiments, a bypass assembly317 includes a ferromagnetic core and pathways along the longitudinaldirection of the bypass assembly that allow fluid to flow from one endof the assembly to the other. In FIGS. 3C-1 and 3C-2, ferromagnetic core355 is surrounded by concentric tubes 361 held in place by ribs 362.Fluid flows along channels created by concentric tubes 361 and ribs 363.In FIGS. 3D-1 and 3D-2, ferromagnetic core 355 is surrounded bylongitudinal tubes 363 in one or more layers, enclosed by a non-magneticbody 364. Fluid flows through tubes 363. In FIGS. 3E-1 and 3E-2,ferromagnetic core 355 is surrounded by one or more laminated sheets 365having channels 366, which can be formed by laminating a channeled sheet367 to a flat sheet 368. Laminated sheet 365 is then wound aroundferromagnetic core 355. Additional sheets can be wound around an innersheet to provide multiple channels through which fluid can flow. InFIGS. 3F-1 and 3F-2, ferromagnetic core 355 is surrounded by a porousmaterial 369, which allows fluid to flow through. In FIG. 3G, core 355is made of a ferromagnetic porous (sintered) material. Thus, core 355functions as the path for both the magnetic flux as well as the fluidflow through bypass assembly 317.

Going back to the embodiment of FIGS. 3B-1 and 3B-2, the fluid flowsalong longitudinal flow groves along the outer circumference of bypassassembly 317. Fluid also flows through distribution holes 318 to a flowsensor input line 319 formed within block 320. Input line 319 directsthe flow to a sensor unit 322, which is secured to block 320 by screws323 and two O-rings 324 or other appropriate seals. One O-ring 324 sealsthe interface between sensor unit 322 and input line 319 of block 320and second O-ring 324 seals the interface between sensor unit 322 and anoutput line 325 formed within block 320. Fluid from output line 325 andbypass assembly 317 travels through a plunger button assembly capturespacer 326, typically made of ferromagnetic material, a plunger buttonassembly 327, (which includes a plunger made of ferromagnetic material,a spring, and a sealing surface), a plunger button pre-tension spacer328, an orifice plate 329 typically made of non-magnetic material, andan orifice metal O-ring 330 or other seal, and out through opening 316in output fitting 314. Plunger button assembly 327 and orifice plate 329are shown in greater detail in FIG. 6A. Plunger button assembly capturespacer 326 secures plunger button assembly 327, spacer 328, orificeplate 329, and O-ring 330 within a cavity in output magnetic flux plate315.

In addition, mass flow controller 300 of the present invention includesa magnetic field generating unit 340. Magnetic field generating unit 340includes a coil 341 and a core 342 inserted into a cylindrical openingwithin coil 341. Core 342 is a cylindrical plug, typically made of aferromagnetic material, which is inserted into openings in the upperportion of input magnetic flux plate 312 and output magnetic flux plate315. Magnetic flux generated by unit 340 is directed down through inputmagnetic flux plate 312, to bypass assembly 317, to plunger buttonassembly 327, and back up through output magnetic flux plate 315. FIG.3H shows the magnetic flux path of controller 300. As seen in FIG. 3H,the magnetic flux travels substantially with the fluid flow within thebody of controller 300, i.e., from input magnetic flux plate 312 andthrough bypass assembly 317 to output magnetic flux plate 315. This iscontrasted with the magnetic flux path of conventional controllers, suchas shown in FIG. 1B.

FIG. 5 is a sectional view of mass flow controller 300 along sectionalline A-A′ of FIG. 3A. FIG. 5 shows that sensor unit 322 is rotatedapproximately 90° from the orientation of conventional mass flowcontroller 10 shown in FIGS. 1A and 2. In other words, fluid flowingthrough sensor unit 322 is orthogonal to the flow direction of the fluidthrough bypass assembly 317 according to the present invention, whereasthe flow directions are parallel with the controller shown in FIGS. 1Aand 2. Sensor unit 322 is a conventionally known and used thermal massflow sensor. The majority of the fluid flows through bypass assembly 317along flow grooves 350 formed longitudinally on the outer surface ofbypass assembly 317. Some of the fluid flows from distribution holes 318to flow sensor input line 319 and into a flow sensor tube 344. Sensortube 344 has wrapped around its outside a first heater/sensor coil 345and a second heater/sensor coil 346, which are connected to terminals347.

Passing current through first coil 345 heats the fluid as it passesthrough sensor tube 344 in the vicinity of first coil 345. Current isalso passed through second coil 346 wrapped around sensor tube 344 inthe downstream flow direction of the fluid, i.e., towards output line325. As the fluid passes second coil 346, it gets hotter. However, theamount of heat transferred from coils 345 and 346 to the fluid isdifferent because the fluid temperature is different at coils 345 and346. This in turn changes the relative resistance of coils 345 and 346,which is measured as a voltage differential in an electrical bridge(i.e., a Wheatstone bridge). This voltage differential corresponds tothe mass flow amount of fluid passing through sensor tube 344, and,proportionately, through bypass assembly 317. Controller unit 300includes electronic circuitry, not shown, to calculate the mass flowbased upon the sensed change in voltage. A servo control section ofcontroller 300 then generates a current signal for magnetic fieldgenerating unit 340, which in turn generates magnetic flux proportionalto the signal to move plunger button assembly 327 to control the flow.The servo control system generates current through the coil to generatesufficient magnetic flux until the error signal is minimized orapproximately zero. Such systems are conventional and known to thoseskilled in the art.

FIG. 6A shows, in more detail, plunger button assembly 327 and orificeplate 329 according to one embodiment. Orifice plate 329 is generallyflat on both faces, with the face toward button assembly 327 having afrusto-conical portion 600. Frusto-conical portion 600 has an opening610 extending through orifice plate 329 such that fluid can flow throughorifice plate 329 to opening 316 in output fitting 314. Plunger buttonassembly 327 has a smooth flat sealing surface 620 that sits on tofrusto-conical portion 600. Plunger button assembly 327 also hasopenings 331 located outside sealing surface 620 for fluid to passthrough. A spacer 328 (shown in FIG. 4) is positioned between plungerbutton assembly 327 and orifice plate 329. Spacer 328 is intended forthe purpose of creating an appropriate amount of compression betweenplunger button assembly 327 and frusto-conical portion 600 by allowing aspring 625 in plunger button assembly 327 to bend to a desired extent byplunger button assembly capture spacer 326. The thinner the spacer 328,the greater the bending of spring 625 in plunger button assembly 327,consequently creating greater compression between plunger buttonassembly 327 and frusto-conical portion 600.

Fluid flows through openings 331 around the outer edges of surface 620as well as around the outer edges of plunger button assembly 327 so thatfluid can flow from bypass assembly 317 to opening 610 of orifice plate329. The amount of fluid flowing into opening 610 depends on thepositioning of plunger button assembly 327 in relation to orifice plate329. As the attractive force to plunger button assembly 327, which iscreated by the magnetic flux, increases, plunger button assembly 327 ismoved away from orifice plate 329, thereby increasing the amount offluid flowing into opening 610. However, as the force decreases, thespring pushes button assembly 327 towards orifice plate 329, therebydecreasing the fluid flow into opening 610. The spring force of thespring should be as small as possible, yet sufficient to seal opening610 to give a zero flow through opening 610. Zero flow means less than0.5% of the mass flow controller range.

FIG. 6B shows another embodiment of plunger button assembly 327 in whicha magnet 626 is attached to the side of plunger button assembly oppositesealing surface 620. By changing the flux direction and magnitudethrough bypass assembly 317, plunger button assembly 327 can be movedeither away from or towards orifice plate 329, thereby controlling theflow of fluid through orifice plate 329. For example, if the magneticflux creates a pole on the end of bypass assembly 317 that is oppositein polarity to magnet 626, the attractive force between bypass assembly317 and plunger button assembly 327 (via magnet 626) will pull plungerbutton assembly 327 away from orifice plate 329, which allows fluid toflow. If the magnetic flux creates a pole that is the same in polarityas magnet 626, bypass assembly 317 will force plunger button assembly327 into orifice plate 329, which will shut off the fluid flow. Thus,depending on the magnitude and direction of the flux and the strength ofmagnet 626, a desired fluid flow can be obtained.

In the above described embodiments, opening 610 in orifice plate 329 isa central through hole. However, in other embodiments, opening 610 canbe an annular ring of slots 700 (shown in FIG. 7A) or holes 710 (shownin FIG. 7B), or a combination of both. In these embodiments, the annularring of holes or slots extend through protruded portions 720 of orificeplate 329, shown in FIG. 7C. Plunger button assembly 327 has a centralhole 730 or slots (not shown) and sealing surface 740, which abutsagainst protruded portions 720 of orifice plate 329. Without anymagnetic flux, protruded portions 720 are sealed against sealing surface740, thereby preventing fluid from flowing through the holes or slots inorifice plate 329. When magnetic flux is generated, plunger buttonassembly 327 is pulled away from orifice plate 329 to allow fluid flowthrough orifice plate 329. Fluid flows through hole 730 of plungerbutton assembly 327 and holes or slots 750 on the outer edge of sealingsurface 740 as well as from the outer perimeter of plunger buttonassembly 327 to the openings of orifice plate 329.

The size and number of slots 700 or holes 710 can be chosen to make themass flow controller for a desired flow rate. For a given flow rate, thearea of the slots (FIG. 7A) or holes (FIG. 7B) should be minimized toreduce the back pressure, resulting in less force required (lessmagnetic flux and therefore less current required) to move plungerbutton assembly 327. However, this area must not be minimized to theextent that choking occurs when fluid is attempting to pass throughorifice plate 329. Choking can also occur in the peripheral area of theslots or holes. Therefore, the peripheral area of the slots or holesshould be greater than or equal to the cross-sectional area of the slotsor holes. Referring to FIGS. 7A-7C, the peripheral area can be definedas the perimeter of the slots or holes times a displacement distance d.Distance d is the maximum distance between plunger button assembly 327and the end of protruded portions 720 for a given flow rate, as shown inFIG. 7C.

Therefore, for a given flow rate and cross-sectional area of slots 700,the peripheral area of the slots can be made equal to or greater thanthe cross-sectional area of the slots by either increasing the perimeterof the slots or increasing the distance d. Increasing distance drequires more magnetic force to achieve the desired flow rate. On theother hand, increasing the perimeter of the slots, which can be done byincreasing the length of the slots and decreasing the width of theslots, allows the peripheral area of the slots to be increased withoutchanging the cross-sectional area of the slots. Consequently, the backpressure is not adversely increased or affected. However, the sameeffect cannot be realized by using holes instead of slots becauseincreasing the perimeter or circumference of the holes also increasesthe cross-sectional area of the holes.

FIG. 8 shows another embodiment of the present invention, in whichbypass assembly 317 is made of a magneto-restrictive material, insteadof a ferromagnetic material described above. The end of bypass assembly317 facing output magnetic flux plate 315 is secured to a sealing device800 having holes 805 for fluid to flow through and a sealing area 810that abuts orifice plate 329 to prevent fluid from flowing throughopening 610 in orifice plate 329. In the normal biased position, sealingdevice 800 abuts orifice plate 329 when sufficient magnetic flux isgenerated to seal opening 610. Magnetic flux travels from input magneticflux plate 312 toward output magnetic flux plate 315 through bypassassembly 317 and sealing device 800. When the magnetic flux is reduced,the magneto-restrictive material constricts, which allows fluid to flowthrough opening 610 in orifice plate 329. Then, when the magnetic fluxis increased, bypass assembly 317 expands until sealing device 800 sealsopening 610. This allows plunger button assembly 327 and plunger buttonassembly pre-tension spacer 328 of FIG. 4 to be eliminated.

In the above described embodiments, the magnetic flux travels throughbypass assembly 317. In other embodiments, shown in FIGS. 9 and 10, themagnetic flux path travels through the body of the mass flow controller.In FIG. 9, the magnetic flux path (shown as a solid black line) travelsthrough core 342, along input magnetic flux plate 312, through masscontroller block 320, which in this embodiment is typically made of aferromagnetic material, through plunger button assembly 327 and back upthrough output magnetic flux plate 315. A magnetic flux separator plateor washer 910, typically made of a non-magnetic material, is locatedbetween mass controller block 320 and output magnetic flux plate 315 sothat the magnetic flux travels through plunger button assembly 327 tocontrol the fluid flow through orifice plate 329. In FIG. 10, coil 341is wound around mass controller block 320. Mass controller block 320,typically made of a ferromagnetic material, encloses bypass assembly317. An outer cover 100, typically made of a ferromagnetic material,encloses coil 341 and block 320. Similar to FIG. 9, magnetic fluxseparator plate or washer 910 separates mass controller block 320 fromoutput magnetic flux plate 315. Accordingly, as shown in FIG. 10, thegenerated magnetic flux (shown as a solid black line) travels throughblock 320 to plunger button assembly 327, up through output magneticflux plate 315, along outer cover 100, and down through input magneticflux plate 312. Note that in the embodiments shown in FIGS. 9 and 10,fluid flows through sensor section 20 (FIGS. 1A and 1B) parallel to theflow of fluid through bypass assembly 317. However, the embodimentsshown in FIGS. 9 and 10 are also suitable with sensor unit 322 (FIGS. 3Aand 5) that allows fluid to flow perpendicular to the flow of fluidthrough bypass assembly 317.

FIGS. 11-19 show an assembled mass flow controller 920 according toanother embodiment of the present invention, with FIG. 14 showing anexploded view of parts of mass flow controller 920, rotated 90°, fromFIG. 11. Referring to FIGS. 11 and 14, mass flow controller 920 hasthree main sections: a controller block section 921, a bypass/valvesection 922, and a sensor section 923. Bypass/valve section 922 with asolenoid core 924 and a solenoid coil 925 are contained within blocksection 921. A cover 926 encloses an electronic control printed circuitboard (PCB) 927 and sensor section 923. Mass flow controller 920 isattached and sealed to a surface mount block, such as by screws 928(FIG. 13) and fluid input/output seals 929.

Referring to FIG. 11, fluid enters through an input port 930 and flowsthrough a channel 931 into an input plenum 932 located within block 921,which is typically made of a non-ferromagnetic material. There, thefluid is split, with a majority of the fluid flowing along longitudinalgrooves/channels 933 (FIGS. 14-16) formed in the generally cylindricalouter surface of a bypass/valve body 934, typically made from aferromagnetic material. In various embodiments, grooves/channels 933 canbe formed directly on bypass/valve body 934 (FIG. 14), on a sleeve 935(FIG. 15), within a sleeve when the sleeve is a porous material thatacts as grooves/channels 933, or on the inner surface of block 921 (FIG.16). Bypass/valve assembly 922, which includes bypass/valve body 934, isattached to block 921, such as by screws 936 (FIG. 13) and seals 937 and967 (FIGS. 11 and 14). Thus, in bypass/valve assembly 922 within block921, the fluid flows from fluid input port 930 to fluid input plenum 932to an output plenum 938.

Referring to FIGS. 11-14 and 19, sensor section 923 is attached tobypass/valve assembly 922, such as by screws 939 and seals 940, and canbe mounted in any 360° orientation substantially perpendicular to theflux path, as shown in FIG. 19. Sensor section 923 includesconventionally known and used thermal mass flow sensors. Referring toFIG. 12, the smaller portion of the split fluid flows through channel941 located within bypass/valve body 934 into a sensor tube 942 andexits from sensor tube 942 into channel 943, located in bypass/valvebody 934 and flows through channel 944 located within block 921, finallymeeting the major portion of the split fluid at the output end of thebypass/valve assembly 922 at output plenum 938. Sensor tube 942 haswrapped around its outside a first heater/sensor coil 945 and connectedto terminals 946.

Passing current through first coil 945 heats the fluid as it passesthrough sensor tube 942 in the vicinity of first coil 945. Current isalso passed through a second coil 947 wrapped around sensor tube 942 inthe downstream flow direction of the fluid, i.e., towards channel 943.As the fluid passes second coil 947, it gets hotter. However, the amountof heat transferred from coils 945 and 947 to the fluid is differentbecause the fluid temperature is different at coils 945 and 947. This inturn changes the relative resistance of coils 945 and 947, which ismeasured as a voltage differential in an electrical bridge (e.g., aWheatstone bridge). This voltage differential corresponds to the massflow amount of fluid passing through sensor tube 942, and proportionallythrough bypass/valve assembly 922. Mass flow controller 920 includeselectronic control PCB 927 to calculate the mass flow based upon thesensed change in voltage.

Bypass/valve assembly 922 contains core 924, typically made from aferromagnetic material, surrounded by solenoid coil 925. One end of core924 is in intimate contact with a valve pole 948, typically made from aferromagnetic material. The other end of core 924 is in intimate contactwith a solenoid cap 949, typically made from a ferromagnetic material.Cap 949, in turn, is in intimate contact with bypass/valve body 934.Valve pole 948 is separated from bypass/valve body 934 by a fluxisolation ring 950, typically made from a non-ferromagnetic material.

An electronic servo control section on PCB 927 generates a currentsignal (depending upon the actual flow and the desired flow) forsolenoid coil 925, which in turn generates magnetic flux proportional tothe signal to move a plunger button assembly 951 (shown in greaterdetail in FIG. 17) to control the flow, as discussed in more detailbelow. The servo control system generates current through coil 925 togenerate sufficient magnetic flux until the error signal(differencebetween the desired flow and actual flow) is minimized or approximatelyzero.

An orifice plate 952, as shown in FIG. 18, typically made of nonferromagnetic material, is generally flat on both faces, with the facetowards plunger button assembly 951 having a frusto-conical portion 953.Frusto-conical portion 953 has an opening 954 extending through orificeplate 952, such that fluid can flow through orifice plate 952 to a fluidoutput channel 955 into an output port 956. Plunger button assembly 951,as shown in FIG. 17, has a smooth flat sealing surface 957 that sits onto frusto-conical portion 953. A spring pretension spacer 958 ispositioned between plunger button assembly 951 and orifice plate 952, asshown in FIGS. 11 and 14. Spacer 958 is intended for the purpose ofcreating an appropriate amount of compression between plunger buttonassembly 951 and frusto-conical portion 953 by allowing a spring 959 inplunger button assembly 951 to bend to a desired extent by a plungerbutton capture spacer 960. The thinner the spacer 958, the greater thebending of spring 959 in plunger button assembly 951, consequentlycreating greater compression between plunger button assembly 951 andfrusto-conical portion 953.

From output plenum 938, fluid flows through grooves/channels 961 (FIG.18) formed into orifice plate 952 and into opening 954. The amount offluid flowing into opening 954 depends on the positioning of plungerbutton assembly 951 in relation to orifice plate 952. As the attractiveforce to plunger button assembly 951, which is created by the magneticflux, increases, plunger button assembly 951 is moved away from orificeplate 952, thereby increasing the amount of fluid flowing into opening954. However, as the force decreases, spring 959 pushes plunger buttonassembly 951 towards orifice plate 952, thereby decreasing the fluidflow into opening 954. The regulated fluid from opening 954 then flowsthrough a fluid output channel 955 and exits from output port 956.

Although the invention has been described with reference to particularembodiments, the description is only an example of the invention'sapplication and should not be taken as a limitation. For example, theabove description describes magnetic flux traveling from the input tothe output. However, the magnetic flux can also travel from the outputto the input along the direction of the bypass assembly for controllingthe fluid flow. The concepts described above can then be modified toopen or close the path of the fluid in response to the presence of themagnetic flux. Consequently, various adaptations and combinations offeatures of the embodiments disclosed are within the scope of theinvention as defined by the following claims.

I claim:
 1. A mass flow controller, comprising: a flow input portlocated on a lower end of the controller; a flow output port located onthe lower end of the controller; a sensor unit in fluid connection withthe input port and the output port; a first channel for carrying a firstamount of fluid from the input port to the output port; a second channelfor carrying a second amount of fluid through the sensor unit, whereinthe second amount is less than the first amount; an orifice assemblycoupled to the output port, wherein the orifice assembly has at leastone orifice opening; a magnetic field generator coupled between theorifice assembly and the sensor, wherein the magnetic field generator,in response to the sensor unit, generates a magnetic flux in a directionfrom the sensor unit to the orifice assembly to allow flow through theat least one orifice opening; and a bypass assembly coupled between thesensor unit and the orifice assembly, wherein the bypass assemblycomprises grooves to allow fluid to flow through, and wherein themagnetic flux travels through the bypass assembly.
 2. A method forcontrolling flow through a mass flow controller having a flow input, aflow output, a sensor unit, and a bypass assembly and a magnetic fieldgenerator coupled between the sensor unit and the flow input and output,the method comprising: introducing a fluid into the flow input;generating an electrical signal, dependent upon a desired flow rate anda measured flow rate, to the magnetic field generator; generating amagnetic flux, dependent on the electrical signal, traveling in adirection approximately parallel to the bypass assembly; in response tothe magnetic flux, adjusting the position of a sealing mechanismrelative to an orifice to adjust the flow rate through the orifice; anddelivering the fluid out from the flow output in a direction opposite ofthe fluid introduction.
 3. The method of claim 2, further comprisingdirecting a flow through the sensor unit approximately perpendicular tothe flow direction through the bypass assembly.
 4. The method of claim2, wherein the adjustment of the sealing mechanism is in a directionapproximately parallel to the flow direction.
 5. The method of claim 2,wherein in the absence of the magnetic flux, the sealing mechanism sealsthe orifice.
 6. The method of claim 2, wherein the magnetic flux travelsthrough the bypass assembly to pull the sealing mechanism away from theorifice.
 7. The method of claim 2, wherein the magnetic flux travelsthrough the bypass assembly.
 8. A mass flow controller, comprising: aflow input port located on a lower end of the controller; a flow outputport located on the lower end of the controller; a sensor unit in fluidconnection with the input port and the output port; a first channel forcarrying a first amount of fluid from the input port to the output port;a second channel for carrying a second amount of fluid through thesensor unit, wherein the second amount is less than the first amount; anorifice assembly coupled to the output port, wherein the orificeassembly has at least one orifice opening; a magnetic field generatorcoupled between the orifice assembly and the sensor, wherein themagnetic field generator, in response to the sensor unit, generates amagnetic flux in a direction from the sensor unit to the orificeassembly to allow flow through the at least one orifice opening; and abypass assembly coupled between the sensor unit and the orificeassembly, wherein the bypass assembly comprises pathways to allow fluidto flow through, and wherein the magnetic flux travels through thebypass assembly.